Cancer is characterized by uncontrolled cell growth which occurs when the normal regulation of cell proliferation is lost. This loss often appears to be the result of dysregulation of the cellular pathways involved in cell growth and division, apoptosis, angiogenesis, tumor invasion and metastasis.
Genistein, 4′,5,7-trihydroxyisoflavone-5,7-dihydroxy-3-(4-hydroxyphenyl)-4H-1-benzopyran-4-one, (shown below), is a natural compound present in plants such as soy. Genistein's potential role in the prevention and treatment of a number of human diseases
including cancer has been extensively studied. Genistein is a BCS class II isoflavone that is commercially available from a number of sources including LC Laboratories, Woburn, Mass. The cellular targets for genistein and the signaling pathways regulated by genistein have been identified and those related to cancer include targets and pathways important for cell growth and division, apoptosis, angiogenesis, tumor invasion and metastasis. In addition to the inherent anti-tumor effects of genistein itself, studies have shown that genistein also potentiates, or accentuates, the anti-tumor effects of several clinically used chemotherapeutic agents both in vitro in human cancer cell lines and in vivo in animal models of cancer. From a therapeutic perspective, these data are interesting as chemotherapy is the cornerstone in the treatment of most solid tumors.
Genistein is practically insoluble in water but has high cell membrane permeability. Low water solubility and slow dissolution rate are often limiting factors responsible for the low bioavailability of pharmaceutical compounds, limiting their application.
Despite the long known fact that genistein has certain properties of anti-cancer drugs, no successful genistein treatment regimens have been, or are, employed in the treatment of cancers. One plausible explanation for this is probably the poor solubility and poor bioavailability as well as the rapid phase II metabolism of genistein in its known form.
Due to the development of the drug discovery strategy over the last 20 years, physicochemical properties of drug development candidates have changed significantly. The development candidates are generally more lipophilic and less water soluble, which creates huge problems for the industry. Research has shown that some drug candidates fail in the clinical phase due to poor human bioavailability and problems with the formulation. Traditional methods to address these problems, without completely redesigning the molecule, include salt selection, producing amorphous material, particle size reduction, pro-drugs, and different formulation approaches. Recently, crystalline forms of active pharmaceutical ingredient (API) have been used to alter the physicochemical properties of the API.
Although therapeutic efficacy is the primary concern for a therapeutic agent, the salt and solid state form (i.e., the crystalline or amorphous form) of a drug candidate can be critical to its pharmacological properties and to its development as a viable API. For example, each salt or each crystalline form of a drug candidate can have different solid state (physical and chemical) properties. The differences in physical properties exhibited by a novel solid form of an API (such as a cocrystal, salt, or polymorph of the original compound) affect pharmaceutical parameters such as storage stability, compressibility and density (important in formulation and product manufacturing), and solubility and dissolution rates (important factors in determining bioavailability). Because these practical physical properties are influenced by the solid state properties of the crystalline form of the API, they can significantly impact the selection of a compound as an API, the ultimate pharmaceutical dosage form, the optimization of manufacturing processes, and absorption in the body. Moreover, finding the most adequate polymorphic form for further drug development can reduce the time and the cost of that development.
Obtaining crystalline forms of an API is extremely useful in drug development. It permits better characterization of the drug candidate's chemical and physical properties. It is also possible to achieve desired properties of a particular API by forming a salt of the API and/or a crystalline salt of the API. Crystalline forms and crystalline salts often have better chemical and physical properties than the free base in its amorphous state. Such salts and crystalline forms may, as with the present invention, possess more favorable pharmaceutical and pharmacological properties or be easier to process than the amorphous polymorphic form. They may also have better storage stability.
One such physical property, which can affect processability, is the flowability of the solid, before and after milling. Flowability affects the ease with which the material is handled during processing into a pharmaceutical composition. When particles of the powdered compound do not flow past each other easily, a formulation specialist must take that fact into account in developing a tablet or capsule formulation, which may necessitate the use of glidants such as colloidal silicon dioxide, talc, starch or tribasic calcium phosphate.
Another potentially important solid state property of an API is its dissolution rate in aqueous fluid. The rate of dissolution of an active ingredient in a patient's stomach fluid may have therapeutic consequences since it impacts the rate at which an orally administered active ingredient may reach the patient's bloodstream.
By forming and/or crystallizing a salt of an API, a new solid state form of the API may have unique properties compared with existing solid forms of the API or its salt. For example, a crystalline salt may have different dissolution and solubility properties than the API itself and can be used to deliver APIs therapeutically. New drug formulations comprising crystalline salts of APIs may have superior properties over existing drug formulations.
A crystalline salt or other crystalline form of an API generally possesses distinct crystallographic and spectroscopic properties when compared to other forms having the same chemical composition. Crystallographic and spectroscopic properties of the particular form are typically measured by X-ray powder diffraction (XRPD) and single crystal X-ray crystallography, among other techniques. Particular crystalline forms often also exhibit distinct thermal behavior. Thermal behavior is measured in the laboratory by such techniques as capillary melting point, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).